Keeping Delaware Bay in the Red Knot’s Journey

Reds knot in flight.

Photo Credit: Gregory Breese, USFWS

One of the longest-distance migrants in the entire animal kingdom is a shorebird that undergoes a round-trip trek of 18,640 miles (30,000 kilometers) each year. The red knot (Caladris canutus rufa) is the focus of extensive conservation attention and collaboration to help restore its declining numbers.

The red knot is a medium-sized shorebird with a wingspan of around 20 inches (51 centimeters). It breeds in the Arctic tundra and winters as far south as Patagonia and the Tierra del Fuego in southern South America. Since the 1980s, the rufa subspecies population has dropped from more than 90,000 to 150,000 birds to between 15,000 and 20,000, according to Kevin Kalasz, the Shorebird Project Coordinator for the Delaware Division of Fish and Wildlife. That means up to 90 percent of the population has been lost.

A candidate for placement on the federal list of threatened and endangered species, the red knot has received assistance from many sources over the past decade in an attempt to reduce threats to its survival and replenish the population.

“In terms of reducing threats, it’s a very good success story,” says Gregory Breese, the project leader at the Delaware Bay Estuary Project of the U.S. Fish and Wildlife Service (Service).

According to Breese, one of the major threats to the red knot population is the overharvesting of horseshoe crabs (Limulus polyphemus) in the Delaware Bay. The mid-Atlantic coast is one of the few areas the birds stop on their 9,300-mile (15,000-km) journey each spring from South America to the Arctic, making available food critical to their survival.

Red Knot tagged on the coast, Mispillion Harbor.

Photo Credit: Greg Breese, USFWS

This stopover coincides with the annual convergence of thousands of horseshoe crabs spawning in the safe, sandy beaches of the Delaware Bay. The birds spend up to two weeks feasting on the horseshoe crab eggs before continuing their migration north. Each red knot can double its weight by eating thousands of the nutrient-rich eggs, preparing for the rest of its journey across the hemisphere.

Because of the human demand and a large increase in the harvest of horseshoe crabs in the 1990s, red knots are having a difficult time finding the food they need to sustain their migration. In addition to their importance in the bait industry, horseshoe crabs are also integral to medical and scientific research.

“Due to concerns over red knots and their declining population, there has been a lot of focus on how to manage horseshoe crabs in order to help the red knot,” says Breese. Some steps that have been taken include changes to harvest limits and the creation of adaptive resource management plans. This means managing horseshoe crabs to better assist red knots by using a scientific model linking the two species. The model reflects how the shorebird could be impacted by various changes made to the horseshoe crab population, allowing scientists and lawmakers to better calculate appropriate regulations concerning harvesting of the crabs.

“That threat, as far as we can tell, has been removed,” according to Breese, yet the red knot population continues to suffer.

Annette Scherer, senior endangered species biologist at the Service’s New Jersey Field Office, cites the lengthy juvenile stage of horseshoe crabs, nine years or more, as a contributing factor to the continued decline of red knot. “The policies have been put in place to provide sufficient food for the migrating red knot, and now we need to wait for the horseshoe crabs to mature and spawn.”

Biologists will continue work to eliminate threats to the red knot during their epic migration, and assess the need to add the bird to the threatened and endangered species list. They remain hopeful for the future of this unique shorebird.